Bettina and I had a day trip on the amazingly beautiful Highway 25 from Hollister to King City. We used the Nikon D800 with the AF-S 70-200mm f/2.8 VR II and the Canon 5D Mark III with our trusty 70-200mm f/4 IS. We did not intend to make a comparison but tried to get the pictures we wanted instead. But this allows us to share with you the results (the full resolution processed images are provided). Both worked fine. You can judge yourself. We have no intention to declare a winner if there even is one. Obviously the D800 has higher resolution while the 5D Mark III combo is lighter and would allow faster bursts.
All processing was done in Lightroom 4.1.
Field Shots Nikon D800 and Canon 5D Mark III - Digital Outback Photo